The following relates to the medical arts. It especially relates to prosthetic venous valves for treatment of chronic venous insufficiency, and will be described with particular reference thereto. However, the following will also find application in treatment of venous blood flow problems generally.
Chronic venous insufficiency is a pathologic condition of the skin and subcutaneous tissues of the lower extremities that results from prolonged stasis of venous blood flow. The venous stasis condition is typically brought on by an abnormal venous hypertension that upsets the normal equilibrium of capillary fluid exchange. This venous hypertension manifests pathologically as changes in the skin and subcutaneous tissues, and can lead to conditions such as edema, pigmentation, dermatitis, induration, stasis cellulitis, and stasis ulcerations. Chronic venous insufficiency is typically difficult to treat, often disabling, and negatively impacts the patient's quality of life.
The most common cause of venous hypertension is degradation of the functionality of one or more venous valves in the deep veins. These valves ordinarily function as “check valves” to prevent backflow of venous blood. However, degraded venous valves are unable to completely block backflow of venous blood, resulting in development of venous hypertension and stasis. The venous hypertension and stasis, in turn, leads to additional distention of the vein and further degradation of the valve.
Various medical therapies are used to treat chronic venous insufficiency. In the lower extremities, compression stockings or boots are used to promote flow of venous blood toward the heart. Surgical interruption of perforator veins in the regions of hypertension has been used to decrease the symptoms of chronic venous insufficiency. In some cases, the degraded venous valve can be surgically repaired.
In another approach, a vein valve is transplanted from a healthy region into the region suffering from chronic venous insufficiency. For example, venous valves in the arm can be transplanted into the leg. This approach presupposes that the patient has healthy venous valves available for transplant. Patients suffering from chronic venous insufficiency often also suffer from other vascular and/or coronary diseases, and so it may be undesirable to transplant healthy venous tissue that may be needed for later bypass procedures.
To address these concerns, both bovine and sheep vein valves have been used as substitutes for human vein valves in transplantation procedures. However, availability of suitably prepared animal vein valves, interspecies tissue compatibility, and other concerns arise in such procedures.
Attempts have also been made to replace degraded venous valves with prosthetic replacements. Existing prosthetic venous valve designs have generally been modeled on prosthetic cardiac valve designs. Prosthetic cardiac valves are normally closed, and only open in response to the substantial blood pressures generated by the beating heart. Such normally closed designs have been successful in the cardiac environment; however, they generally exhibit poor performance in the low flow, low pressure venous system that fosters thrombosis and intimal hyperplasia of implanted prosthetic devices.
Venous blood pressures are lower than those encountered in the heart, and the venous valve must remain open under low blood pressure and flow. Infrequent venous valve cycling and low venous blood pressure and flow produces substantial residency times for blood contacting the prosthetic venous valve. Flow resistance caused by a normally closed or incompletely open venous valve replacement further increases blood residency time and can lead to blood clotting.
Acosta et al., U.S. Pat. No. 6,958,076 (previously published as U.S. Publ. Appl. 2002/0177894 A1, which is incorporated herein by reference in its entirety), discloses various normally open venous valves that represent substantial improvements over previous normally closed prosthetic venous valves that are modeled after heart valves. These normally open venous valves more closely functionally mimic natural human venous valves. They provide low resistance to blood flow in the normal open condition, which reduces the residency time of blood contacting the venous valve replacement. This in turn reduces the likelihood of blood clot formation at or near the venous valve replacement.
The following contemplates improved apparatuses and methods that overcome the above-mentioned limitations and others.